DESCRIPTION: The Gene Manipulation Core provides investigators with central services for generation of gene targeting and transgenic mice. Its services include establishment and maintenance of embryonic stem cell cultures, blastocyst injections, transgenic injections, and supplying reagents and consultation for gene targeting and transgenic studies. The Core will provide services for MRRC investigators as well as non Center investigators, although with a higher service fee for the latter. Access to the Core services is based on a sign-up system followed by a review by the Core Director and the Senior Research Technologist. The Users Committee meets periodically with the Core Director and Senior Research Technologist to ensure the quality of the services and effectiveness of the core function. The Users Committee also reviews surveys by users to make needed recommendations.